Yesterday we got a Pure Storage All Flash Array for testing. As the name implies this is all about Flash storage. What makes Pure Storage different from other vendors is that you don’t buy just a storage box and then pay the usual maintenance costs but you pay for a storage subscription which should keep your storage up to date all the time. The promise is that all the components of the array get replaced by the then current versions over time without forcing you to re-buy. Check the link above for more details on the available subscriptions. This is the first post and describes the setup we did for connecting a PostgreSQL VMWare based machine to the Pure Storage box. The PostgreSQL server will be running as a virtual machine in VMWare ESX and connect over iSCSI to the storage system.

As usual we used CentOS 7 for the PostgreSQL server:

[root@pgpurestorage ~]$ cat /etc/centos-release
CentOS Linux release 7.3.1611 (Core) 
[root@pgpurestorage ~]$ uname -a
Linux 3.10.0-514.el7.x86_64 #1 SMP Tue Nov 22 16:42:41 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

We have 4 vCPUs:

[root@pgpurestorage ~]$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                4
On-line CPU(s) list:   0-3
Thread(s) per core:    1
Core(s) per socket:    1
Socket(s):             4
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 79
Model name:            Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz
Stepping:              1
CPU MHz:               2399.583
BogoMIPS:              4799.99
Hypervisor vendor:     VMware
Virtualization type:   full
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              35840K
NUMA node0 CPU(s):     0-3

… and 8GB of memory:

[root@pgpurestorage ~]$ cat /proc/meminfo | head -5
MemTotal:        7994324 kB
MemFree:         7508232 kB
MemAvailable:    7528048 kB
Buffers:            1812 kB
Cached:           233648 kB


Because by default you’ll get the “virtual-guest” tuned profile when you install CentOS in a virtualized environment we created our own and switched to the same:

root@:/home/postgres/ [] tuned-adm active
Current active profile: virtual-guest
root@:/home/postgres/ [] tuned-adm profile dbi-postgres
root@:/home/postgres/ [] tuned-adm active
Current active profile: dbi-postgres
root@:/home/postgres/ [] cat /usr/lib/tuned/dbi-postgres/tuned.conf | egrep -v "^#|^$"
summary=dbi services tuned profile for PostgreSQL servers
kernel.sched_min_granularity_ns = 10000000
kernel.sched_wakeup_granularity_ns = 15000000

To gather statistics we created a cronjob:

root@:/home/postgres/ []  crontab -l
* * * * * /usr/lib64/sa/sa1 -S XALL 60 1

PostgreSQL was installed from source with what was committed to the source tree as of today with the following options:

[postgres@pgpurestorage postgresql]$ PGHOME=/u01/app/postgres/product/10/db_0
[postgres@pgpurestorage postgresql]$ SEGSIZE=2
[postgres@pgpurestorage postgresql]$ BLOCKSIZE=8
[postgres@pgpurestorage postgresql]$ WALSEGSIZE=64
[postgres@pgpurestorage postgresql]$ ./configure --prefix=${PGHOME} \
>             --exec-prefix=${PGHOME} \
>             --bindir=${PGHOME}/bin \
>             --libdir=${PGHOME}/lib \
>             --sysconfdir=${PGHOME}/etc \
>             --includedir=${PGHOME}/include \
>             --datarootdir=${PGHOME}/share \
>             --datadir=${PGHOME}/share \
>             --with-pgport=5432 \
>             --with-perl \
>             --with-python \
>             --with-tcl \
>             --with-openssl \
>             --with-pam \
>             --with-ldap \
>             --with-libxml \
>             --with-libxslt \
>             --with-segsize=${SEGSIZE} \
>             --with-blocksize=${BLOCKSIZE} \
>             --with-wal-segsize=${WALSEGSIZE}  \
>             --with-extra-version=" dbi services build"

For being able to connect to the Pure Storage box you’ll need the iSCSI IQN:

root@:/home/postgres/ [] cat /etc/iscsi/initiatorname.iscsi

Knowing the IQN (InitiatorName) we can logon to the Pure Storage console for adding our host, creating a volume and attaching the volume to the host:

Thu May 04 11:44:10 2017
Welcome pureuser. This is Purity Version 4.8.8 on FlashArray dbipure01
pureuser@dbipure01> purehost create --iqn pgpurestorage
Name           WWN  IQN                               
pgpurestorage  -
pureuser@dbipure01> purevol create --size 500G volpgtest
Name       Size  Source  Created                   Serial                  
volpgtest  500G  -       2017-05-04 11:46:58 CEST  BA56B4A72DE94A4400011012
pureuser@dbipure01> purehost connect --vol volpgtest pgpurestorage
Name           Vol        LUN
pgpurestorage  volpgtest  1  

The Pure Storage system has two controllers ( and so we should be able to ping them:

root@:/home/postgres/ [] ping
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=63 time=2.53 ms
64 bytes from icmp_seq=2 ttl=63 time=0.816 ms
64 bytes from icmp_seq=3 ttl=63 time=0.831 ms
root@:/u02/pgdata/pgpure/ [] ping
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=63 time=0.980 ms
64 bytes from icmp_seq=2 ttl=63 time=0.848 ms

Ok for the connectivity so a discover should work as well:

root@:/home/postgres/ [] iscsiadm -m discovery -t st -p,1,1
root@:/home/postgres/ [] iscsiadm -m node,1,1

Fine as well, so login:

root@:/home/postgres/ [] iscsiadm -m node --login 
Logging in to [iface: default, target:, portal:,3260] (multiple)
Logging in to [iface: default, target:, portal:,3260] (multiple)
Login to [iface: default, target:, portal:,3260] successful.
Login to [iface: default, target:, portal:,3260] successful.
root@:/home/postgres/ [] iscsiadm -m session -o show 
tcp: [13],1 (non-flash)
tcp: [14],1 (non-flash)

The new device is available (sdb) from now on:

root@:/home/postgres/ [] ls -la /dev/sd*
brw-rw----. 1 root disk 8,  0 May  4 13:23 /dev/sda
brw-rw----. 1 root disk 8,  1 May  4 13:23 /dev/sda1
brw-rw----. 1 root disk 8,  2 May  4 13:23 /dev/sda2
brw-rw----. 1 root disk 8, 16 May  4 13:23 /dev/sdb
brw-rw----. 1 root disk 8, 32 May  4 13:23 /dev/sdc

LVM setup:

root@:/home/postgres/ [] pvcreate /dev/sdb
  Physical volume "/dev/sdb" successfully created.
root@:/home/postgres/ [] vgcreate vgpure /dev/sdb
  Volume group "vgpure" successfully created
root@:/home/postgres/ [] lvcreate -L 450G -n lvpure vgpure
  Logical volume "lvpure" created.
root@:/home/postgres/ [] mkdir -p /u02/pgdata
root@:/home/postgres/ [] mkfs.xfs /dev/mapper/vgpure-lvpure 
meta-data=/dev/mapper/vgpure-lvpure isize=512    agcount=4, agsize=29491200 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=117964800, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=57600, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

root@:/home/postgres/ [] echo "/dev/mapper/vgpure-lvpure  /u02/pgdata  xfs defaults,noatime 0 0" >> /etc/fstab
root@:/home/postgres/ [] mount -a
root@:/home/postgres/ [] df -h
Filesystem                         Size  Used Avail Use% Mounted on
/dev/mapper/cl_pgpurestorage-root   26G  2.0G   25G   8% /
devtmpfs                           3.9G     0  3.9G   0% /dev
tmpfs                              3.9G     0  3.9G   0% /dev/shm
tmpfs                              3.9G  8.5M  3.9G   1% /run
tmpfs                              3.9G     0  3.9G   0% /sys/fs/cgroup
/dev/sda1                         1014M  183M  832M  19% /boot
tmpfs                              781M     0  781M   0% /run/user/1000
/dev/mapper/vgpure-lvpure          450G   33M  450G   1% /u02/pgdata
root@:/home/postgres/ [] chown postgres:postgres /u02/pgdata

Initialized the PostgreSQL cluster:

postgres@pgpurestorage:/home/postgres/ [pg10] initdb -D /u02/pgdata/
The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locales
  CTYPE:    en_US.UTF-8
  TIME:     en_US.UTF-8
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

fixing permissions on existing directory /u02/pgdata ... ok
creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... ok
syncing data to disk ... ok

WARNING: enabling "trust" authentication for local connections
You can change this by editing pg_hba.conf or using the option -A, or
--auth-local and --auth-host, the next time you run initdb.

Success. You can now start the database server using:

    pg_ctl -D /u02/pgdata/ -l logfile start

What we changed from the default configuration is:

postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] cat 
# Do not edit this file manually!
# It will be overwritten by the ALTER SYSTEM command.
listen_addresses = '*'
logging_collector = 'on'
log_truncate_on_rotation = 'on'
log_filename = 'postgresql-%a.log'
log_rotation_age = '8d'
log_line_prefix = '%m - %l - %p - %h - %u@%d '
log_directory = 'pg_log'
log_min_messages = 'WARNING'
log_autovacuum_min_duration = '360s'
log_min_error_statement = 'error'
log_min_duration_statement = '5min'
log_checkpoints = 'on'
log_statement = 'ddl'
log_lock_waits = 'on'
log_temp_files = '1'
log_timezone = 'Europe/Zurich'
client_min_messages = 'WARNING'
wal_level = 'replica'
hot_standby_feedback = 'on'
max_wal_senders = '10'
cluster_name = 'pgpure'
max_replication_slots = '10'

Calculating the minimum required amount of huge pages for the PostgreSQL instance:

postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] head -1 $PGDATA/
postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] grep ^VmPeak /proc/3662//status
VmPeak:	 2415832 kB
postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] echo "2415832/2048" | bc

Set it slightly higher:

postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] sudo sed -i 's/vm.nr_hugepages=1024/vm.nr_hugepages=1200/g' /usr/lib/tuned/dbi-postgres/tuned.conf
postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] sudo tuned-adm profile dbi-postgres
postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] cat /proc/meminfo | grep Huge
AnonHugePages:      6144 kB
HugePages_Total:    1200
HugePages_Free:     1200
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB

To disable transparent huge pages we created a file called “disable-thp.service” (from here):

postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] cat /etc/systemd/system/disable-thp.service
# Disable transparent huge pages
# put this file under:
#   /etc/systemd/system/disable-thp.service
# Then:
#   sudo systemctl daemon-reload
#   sudo systemctl start disable-thp
#   sudo systemctl enable disable-thp
Description=Disable Transparent Huge Pages (THP)

ExecStart=/bin/sh -c "echo 'never' > /sys/kernel/mm/transparent_hugepage/enabled && echo 'never' > /sys/kernel/mm/transparent_hugepage/defrag"


Then reload the systemd daemon and start and enable the service:

postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] sudo systemctl daemon-reload
postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] sudo systemctl start disable-thp
postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] sudo systemctl enable disable-thp

To verify:

postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] cat /sys/kernel/mm/transparent_hugepage/enabled
always madvise [never]
postgres@pgpurestorage:/u02/pgdata/pgpure/ [pgpure] cat /sys/kernel/mm/transparent_hugepage/defrag 
always madvise [never]

For being sure that PostgreSQL really will use the huge pages set huge_pages to ‘on’ as this will prevent PostgreSQL from starting when the required pages can not be allocated:

pgpurestorage/postgres MASTER (postgres@5432) # alter system set huge_pages='on';
Time: 2.417 ms

… and then restart the instance. When all is fine PostgreSQL will come up.

Finally to close this setup post here are some screenshots of the Pure Storage Management Web Console. The first one shows the “Storage” tab where you can see that the volume “volpgtest” is mapped to my host “pgpurestorage”.

The name you give the server is not important. The important information is the mapping of the “Host Port” which you can see here (this is the iSCSI IQN):


Once your server is connected you can see it in the connection map of the server in the console:

System health:

Last, but not least, here is the dashboard:

Not much traffic right now but we’ll be changing that in the next post.